General Prefs : Internal Frames

All main, document and supportive windows and palettes can be configured to be either independant frames or internal frames inside one encompassing application frame. On Mac OS X users will likely not use internal frames as the native look-and-feel uses independant windows.

On Windows (and probably Linux), people are accustomed to have each application present itself as a big screen filling frame with all its child windows internal to that frame. So the default settings on Windows and Linux is to use internal frames.